Injection moulding apparatus typically comprises fixed and movable load-bearing platens which are adapted to clamp between them respective halves of a two-part mould. By means of an hydraulically or mechanically operated ram, pressure is applied to the movable platen so as to clamp together the two halves of the mould into which molten plastics material is then injected at pressure which can often be very high. In order to ensure that the two sections of the mould are not displaced with respect to each other as a result of the high pressure injection of the plastics material, a high clamping force has to be applied so as to hold together the two sections of the mould.
Hitherto proposed apparatus for achieving these objectives are well known in the art and have been available for many years. Thus, for example, U.S. Pat. No. 3,128,501 (J. E. Borah) describes a power operated multiple press, the principles of which have changed little since the publication of this patent. Borah describes an apparatus which includes fixed and movable platens which are slidably supported with respect to each other by means of four corner posts or tie bars located respectively at the four corners of the two platens, such that the movable platen may slide along these posts towards and away from the fixed platen. The two halves of a mould are substantially symmetrically supported by facing surfaces of the two platens, the clamping force being directed along an axis which is substantially collinear with the axis of symmetry of the mould.
With such known structures, the presence of the four tie bars seriously limits the accessibility of the region between the platens insofar as the introduction and removal of the mould sections are concerned. This limitation is particularly troublesome when one bears in mind that the mould sections can be of significant size, complex shape and significant weight and require to be manoeuvred into position and removed therefrom using mechanical handling equipment. Furthermore, this relative inaccessibility of the clamping space seriously limits the degree of automation which could otherwise be employed in connection with the introduction and removal of the mould sections.
It is an object of the present invention to provide a new and improved clamping assembly for an injection moulding apparatus wherein the above-referred-to disadvantages are significantly reduced.